1. Technical Field
The invention relates to photonic devices. In particular, the invention relates to photonic devices employed as filters and modulators.
2. Description of Related Art
Optical filters and related components such as, but not limited to, optical modulators that employ filtering are critical components in virtually all photonic systems. For example, various forms of filtering are typically employed to separate out individual signals for selective processing from a group of signals carried by a broadband frequency multiplexed optical carrier. Optical filters, like other types of filters, may be generally classified as either broad band or narrow band and may be realized as one of a lowpass filter, a bandpass filter, a band reject or notch filter, and a high pass filter. Of particular interest to many frequency multiplexing applications are narrow bandpass and band reject filters. For example, a narrow bandpass filter may be used to select a particular signal or signal channel from among a group of such signals in a broadband carrier. In another example, a narrowband notch filter may be employed to remove a single signal or signal channel from such a broadband carrier, for example. Similarly, modulators that employ narrowband filtering may selectively modulate such a single signal or signal channel.
A wide variety of filters are used in photonic systems. Recently, guided-mode resonant (GMR) gratings have attracted considerable interest as a means for providing narrowband filtering. GMR gratings may be realized that exhibit a very sharp, narrowband, high-Q coupling between an incident signal and a guided mode of the GMR grating. The coupling has been employed to implement narrowband transmission and narrowband reflection (i.e., rejection) filters. In addition, both transmissive and reflective modulators using GMR gratings have been demonstrated.
Unfortunately, while exhibiting very good coupling in a narrowband frequency band around a GMR resonant frequency of the GMR grating, an out-of-band reflection response of the GMR grating typically degrades significantly away from the GMR resonant frequency. This degradation in the out-of-band reflection response may significantly limit the utility of filters and modulators that are implemented using a GMR grating. Therefore, providing a GMR grating having a relatively wide and flat reflection response out-of-band while still providing high-Q performance in-band would satisfy a long felt need.